Investigation of antimicrobial and antioxidant activities of essential oils extracted from medicinal plants

Essential oils of eleven plants including anise, hyssop, flos lavandulae, pot marigold, fennel, mint, chamomile petal, clary sage, cilantro, herba lippiae and dill were screened for total phenolic content by the Folin-Ciocalteu method, for potential antioxidant activity using the phosphomolybdenum assay and for antiradical activity by the 1,1-diphenyl-2-picryl hydrazyl (DPHH) method. The antimicrobial activity was examined by using agar disc diffusion as well as the minimum inhibitory concentration (MIC) method. The essential oils showed considerable antimicrobial activity against most of the tested microorganisms. The essential oil of dill was very effective in inhibiting the growth of all bacterial strains tested, with a low MIC (125 mu l/ml). Overall, the lowest MIC was found for E. coli O157:H7 and E. coli ATCC 25922 while the highest values were found for S. aureus and L. monocytogenes. The highest total antioxidant capacity as ascorbic acid equivalent (AAE) of 195.27 mg/g was obtained for mint with the phosphomolybdenium assay. The highest percentage of inhibition of DPPH radical was obtained with essential oil from dill (92.70 %). It was followed by radical scavenging activities of essential oils from mint (81.00 %) and anise (71.53 %). Total phenolic content of the essential oils ranged from 2.33 to 695.06 mg gallic acid per 100 g of the samples. Mint and dill had the highest content of total phenols. The essential oils of mint, dill, anise hyssop, and flos lavandulae may prove to be a good source of antioxidant and antimicrobial agents for the food and pharmaceutical industries.